1. Field of the Invention
The present invention relates generally to power supplies using interconnected primary cells and, more particularly, to a three-conductor power transmission interconnect system for series grouped cells which reduces the relative transmission voltage and prevents transmission interruption due to the loss of one or more cells in any group.
2. Description of the Prior Art
Power supplies using a plurality of groups or strings of series-connected primary cells are well known. Conventionally each group is made large enough so that the full required potential is achieved by connecting all the cells in the group in series. Power is achieved by connecting additional groups in parallel across a two-conductor transmission system.
Conventional power transmission techniques employed to reduce transmission losses in such systems normally utilize increased wire sizes and higher transmission voltages. The use of larger wire sizes increases the system costs and higher voltage outputs from the cell strings raise the cell-to-mounting structure insulation or standoff voltage requirements. This also adds to the a cost of the a system.
In some systems the output of the cells is accompanied by high levels of heat such that the cells must continually be cooled. This occurs in the case of some fuel cells and certainly with photovoltaic conversion cells. It is desirable that the amount of electrical insulation required be minimized because the insulation decreases the thermal conductivity between the cells and the cooling medium. Thus, this added insulation necessitated by the high potential to ground of conventional series-connected cell groups causes the cells to operate at a higher than desirable temperature. In some cases, this may create the danger of cell explosion and, in others such as photovoltaic cells, will reduce the cell power output.
Another problem associated with many interconnection systems involves the loss of one or more cells. Conventional systems do not have any isolation protection between groups of cells. Thus, if a short or other failure occurs in one group of cells, the entire power transmission system will be affected and may fail.
These problems have led to a need for a cell interconnecting power transmission system which reduces cell string to mounting surface intrinsic standoff voltage requirements, reduces interconnecting wire resistance power losses for a given interconnecting wire size and which prevents a fault in one group of cells from inhibiting the normal operation of any other such groups in the power supply.